page_title: Water on Mars
section_title: Mars Exploration Rovers
hierarchical_section_title: Water on Mars / Findings by probes / Mars Exploration Rovers
caption_attribution_description: English: This sharp, close-up image taken by the microscopic imager on the Mars Exploration Rover Opportunity's instrument deployment device, or "arm," shows a rock target dubbed "Robert E," located on the rock outcrop at Meridiani Planum, Mars. Scientists are studying this area for clues about the rock outcrop's composition. This image measures 3 centimeters (1.2 inches) across and was taken on the 15th day of Opportunity's journey (Feb. 8, 2004). Deutsch: Hämatitkonkretion, Bildausschnitt 3cm
context_page_description: Almost all water on Mars today exists as ice, though it also exists in small quantities as vapor in the atmosphere. What was thought to be low-volume liquid brines in shallow Martian soil, also called recurrent slope lineae, may be grains of flowing sand and dust slipping downhill to make dark streaks. The only place where water ice is visible at the surface is at the north polar ice cap. Abundant water ice is also present beneath the permanent carbon dioxide ice cap at the Martian south pole and in the shallow subsurface at more temperate conditions. More than 21 million km³ of ice have been detected at or near the surface of Mars, enough to cover the whole planet to a depth of 35 meters. Even more ice is likely to be locked away in the deep subsurface.
  Some liquid water may occur transiently on the Martian surface today, but limited to traces of dissolved moisture from the atmosphere and thin films, which are challenging environments for known life.
context_section_description: The Mars Exploration Rovers, Spirit and Opportunity found a great deal of evidence for past water on Mars. The Spirit rover landed in what was thought to be a large lake bed. The lake bed had been covered over with lava flows, so evidence of past water was initially hard to detect. On March 5, 2004, NASA announced that Spirit had found hints of water history on Mars in a rock dubbed "Humphrey".
  As Spirit traveled in reverse in December 2007, pulling a seized wheel behind, the wheel scraped off the upper layer of soil, uncovering a patch of white ground rich in silica. Scientists think that it must have been produced in one of two ways. One: hot spring deposits produced when water dissolved silica at one location and then carried it to another (i.e. a geyser). Two: acidic steam rising through cracks in rocks stripped them of their mineral components, leaving silica behind. The Spirit rover also found evidence for water in the Columbia Hills of Gusev crater. In the Clovis group of rocks the Mössbauer spectrometer (MB) detected goethite, that forms only in the presence of water, iron in the oxidized form Fe³⁺, carbonate-rich rocks, which means that regions of the planet once harbored water.
  The Opportunity rover was directed to a site that had displayed large amounts of hematite from orbit. Hematite often forms from water. The rover indeed found layered rocks and marble- or blueberry-like hematite concretions. Elsewhere on its traverse, Opportunity investigated aeolian dune stratigraphy in Burns Cliff in Endurance Crater. Its operators concluded that the preservation and cementation of these outcrops had been controlled by flow of shallow groundwater. In its years of continuous operation, Opportunity sent back evidence that this area on Mars was soaked in liquid water in the past.
  The MER rovers found evidence for ancient wet environments that were very acidic. In fact, what Opportunity found evidence of sulphuric acid, a harsh chemical for life. But on May 17, 2013, NASA announced that Opportunity found clay deposits that typically form in wet environments that are near neutral acidity. This find provides additional evidence about a wet ancient environment possibly favorable for life.
caption: Close-up of a rock outcrop.
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